初始化

最简应用

from fastapi import FastAPI
app = FastAPI()

@app.get("/")
async def root():
    return {"message": "Hello, World!"}

运行应用

pip install "fastapi[standard]"
fastapi dev main.py    # dev with auto-reload
fastapi run main.py    # production

核心特性

Async native	async/await，ASGI（Uvicorn）
Auto docs	Swagger UI 在 `/docs`，ReDoc 在 `/redoc`
Type validation	Pydantic 模型验证请求/响应
OpenAPI	自动生成 OpenAPI schema
Dependency injection	内置依赖注入系统

路径操作

HTTP 方法

@app.get("/items")
@app.post("/items")
@app.put("/items/{item_id}")
@app.patch("/items/{item_id}")
@app.delete("/items/{item_id}")

路径参数

@app.get("/users/{user_id}")
async def get_user(user_id: int):
    return {"user_id": user_id}

# Enum constraint
from enum import Enum
class Color(str, Enum):
    red = "red"
    blue = "blue"

状态码与标签

from fastapi import status

@app.post("/items", status_code=status.HTTP_201_CREATED,
          tags=["items"])
async def create_item(item: Item):
    return item

请求体

Pydantic 模型

from pydantic import BaseModel, Field

class Item(BaseModel):
    name: str
    price: float = Field(gt=0, description="Must be positive")
    tags: list[str] = []

嵌套模型

class Address(BaseModel):
    street: str
    city: str
    zip_code: str

class User(BaseModel):
    name: str
    address: Address

在端点中使用

@app.post("/items")
async def create_item(item: Item):
    return {"name": item.name, "price": item.price}

验证特性

Field(gt=0)	大于 0
Field(min_length=1)	最小字符串长度
Field(max_length=100)	最大字符串长度
Field(pattern='^[a-z]+$')	正则模式匹配
Field(default=None)	带默认值的可选字段
EmailStr	邮箱验证（pydantic[email]）

查询参数

基础查询参数

@app.get("/items")
async def list_items(skip: int = 0, limit: int = 10):
    return items[skip : skip + limit]
# GET /items?skip=0&limit=20

查询验证

from fastapi import Query

@app.get("/search")
async def search(
    q: str = Query(min_length=3, max_length=50),
    page: int = Query(default=1, ge=1),
):
    return {"q": q, "page": page}

可选与必填

async def read_items(
    q: str | None = None,   # optional
    name: str = ...,         # required (Ellipsis)
    tags: list[str] = Query(default=[]),
):
    return {"q": q, "name": name}

Header 与 Cookie

from fastapi import Header, Cookie

async def read(
    user_agent: str | None = Header(default=None),
    session_id: str | None = Cookie(default=None),
):
    return {"ua": user_agent}

响应模型

class ItemOut(BaseModel):
    name: str
    price: float

@app.get("/items/{id}", response_model=ItemOut)
async def get_item(id: int):
    return items[id]  # filters out extra fields

多种响应类型

from fastapi.responses import JSONResponse, HTMLResponse

@app.get("/html", response_class=HTMLResponse)
async def get_html():
    return "Hello"

响应模型选项

response_model	用于输出过滤的 Pydantic 模型
response_model_exclude_unset	省略未显式设置的字段
response_model_include	白名单特定字段
response_model_exclude	黑名单特定字段

错误响应

from fastapi import HTTPException

@app.get("/items/{id}")
async def get_item(id: int):
    if id not in items:
        raise HTTPException(status_code=404, detail="Not found")
    return items[id]

依赖注入

函数依赖

from fastapi import Depends

async def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

在端点中使用

@app.get("/users")
async def list_users(db: Session = Depends(get_db)):
    return db.query(User).all()

类依赖

class Pagination:
    def __init__(self, skip: int = 0, limit: int = 10):
        self.skip = skip
        self.limit = limit

@app.get("/items")
async def list_items(pg: Pagination = Depends()):
    return items[pg.skip : pg.skip + pg.limit]

依赖作用域

Depends(func)	端点级依赖
app = FastAPI(dependencies=[...])	所有路由的全局依赖
APIRouter(dependencies=[...])	Router 级依赖
yield	安装/拆卸（DB session、锁）

认证

OAuth2 密码 Bearer

from fastapi.security import OAuth2PasswordBearer

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

@app.get("/users/me")
async def read_me(token: str = Depends(oauth2_scheme)):
    user = decode_token(token)
    return user

JWT Token 流程

from jose import jwt
SECRET = "your-secret-key"

def create_token(data: dict):
    return jwt.encode(data, SECRET, algorithm="HS256")

def decode_token(token: str):
    return jwt.decode(token, SECRET, algorithms=["HS256"])

Token 端点

from fastapi.security import OAuth2PasswordRequestForm

@app.post("/token")
async def login(form: OAuth2PasswordRequestForm = Depends()):
    user = authenticate(form.username, form.password)
    if not user:
        raise HTTPException(status_code=401)
    return {"access_token": create_token({"sub": user.id})}

安全方案

OAuth2PasswordBearer	通过表单登录的 Bearer token
HTTPBasic	基础用户名/密码认证
APIKeyHeader	Header 中的 API key
APIKeyCookie	Cookie 中的 API key

后台任务

简单后台任务

from fastapi import BackgroundTasks def send_email(to: str, body: str): # slow operation runs after response email_client.send(to, body) @app.post("/notify") async def notify(bg: BackgroundTasks): bg.add_task(send_email, "[email protected]", "Hello!") return {"status": "queued"}

依赖中使用后台任务

async def log_request(bg: BackgroundTasks):
    bg.add_task(write_log, "request received")

@app.get("/items", dependencies=[Depends(log_request)])
async def list_items():
    return items

后台任务 vs Worker

BackgroundTasks	响应后的轻量任务（邮件、日志）
Celery / ARQ	需要独立 worker 的重任务
asyncio.create_task	即发即忘的异步协程

中间件

自定义中间件

import time
from starlette.middleware.base import BaseHTTPMiddleware

class TimingMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request, call_next):
        start = time.time()
        response = await call_next(request)
        duration = time.time() - start
        response.headers["X-Process-Time"] = str(duration)
        return response

添加中间件

app.add_middleware(TimingMiddleware)

CORS

from fastapi.middleware.cors import CORSMiddleware

app.add_middleware(
    CORSMiddleware,
    allow_origins=["https://example.com"],
    allow_methods=["*"],
    allow_headers=["*"],
)

内置中间件

CORSMiddleware	跨域资源共享
TrustedHostMiddleware	限制允许的主机名
GZipMiddleware	Gzip 响应压缩
HTTPSRedirectMiddleware	HTTP 重定向到 HTTPS

测试

测试客户端

from fastapi.testclient import TestClient

client = TestClient(app)

def test_read_root():
    resp = client.get("/")
    assert resp.status_code == 200
    assert resp.json() == {"message": "Hello, World!"}

测试 POST

def test_create_item():
    resp = client.post("/items", json={
        "name": "Widget",
        "price": 9.99,
    })
    assert resp.status_code == 201
    assert resp.json()["name"] == "Widget"

覆盖依赖

async def mock_db():
    return FakeDB()

app.dependency_overrides[get_db] = mock_db

def test_with_mock_db():
    resp = client.get("/users")
    assert resp.status_code == 200

异步测试

import pytest
from httpx import AsyncClient, ASGITransport

@pytest.mark.anyio
async def test_async():
    transport = ASGITransport(app=app)
    async with AsyncClient(transport=transport) as ac:
        resp = await ac.get("/")
    assert resp.status_code == 200

FASTAPI 快速参考

Hello